Geoffrey Evans
The University of Newcastle, Chemical Engineering, Faculty Member
Expansion behaviour of a binary solid-liquid fluidised bed (SLFB) system with different initial mass of solids was studied both experimentally and numerically. Three different sizes (3, 5 & 8 mm diameter) of borosilicate glass beads of... more
Expansion behaviour of a binary solid-liquid fluidised bed (SLFB) system with different initial mass of solids was studied both experimentally and numerically. Three different sizes (3, 5 & 8 mm diameter) of borosilicate glass beads of equal density (2230 kgm) were used as fluidised particles. Three different combinations of particle size pairs of both equal and unequal mass ratios were used using a constant liquid (water) superficial velocity of 0.17 ms in all the cases. Numerically, a two dimensional Eulerian-Eulerian (E-E) CFD model incorporating kinetic theory of granular flow (KTGF) was developed to predict the bed expansion behaviour. It was observed that complete bed segregation occurred when the difference between the solid particle diameters was higher while lower difference in particle diameters led to partial bed segregation. The CFD model also predicted these behaviours which were in good agreement with the experimental data.
In this paper, the fluidization of 8 mm glass particles in water has been simulated using a new methodology developed within the DEM framework. In this methodology, random liquid fluctuating velocities are used as direct input into the... more
In this paper, the fluidization of 8 mm glass particles in water has been simulated using a new methodology developed within the DEM framework. In this methodology, random liquid fluctuating velocities are used as direct input into the drag model. The specific aim of this study is to directly compute the granular pressure in a liquid fluidized bed. The granular pressure is defined using the particle-wall collision frequency and the corresponding particle momentum transport during the collision. Initially, we validated our model by comparing the relationship between superficial fluid velocity and bed expansion against the well-known Richardson-Zaki [1] equation. The results demonstrated a good agreement of our model. The granular pressure and temperature, as well as the particle-wall collision frequency, in the liquid fluidized bed were determined for superficial fluid velocities in the range between 0.08 and 0.32 m/s. The granular pressure exhibited a maximum (between 0.3-0.4 solid ...
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Droplet evaporation in fluidized beds is of great interest in applications like fluidized catalytic cracking units. Although a significant number of analyses are available for modelling of droplet vaporization in a fluidized bed, very... more
Droplet evaporation in fluidized beds is of great interest in applications like fluidized catalytic cracking units. Although a significant number of analyses are available for modelling of droplet vaporization in a fluidized bed, very little work has been performed experimentally to measure the vapour concentration followed by numerical validation. In the present work, acetone droplet evaporation in a bubbling fluidized bed is studied experimentally as well as numerically. A liquid jet of acetone is injected into a hot bubbling fluidized bed kept well above saturation temperature of acetone. Nonintrusive Schlieren imaging, based on the difference in refractive index, is used to trace the acetone vapour concentration profile. The bubbling fluidized bed is modelled in an Eulerian framework using a simplistic porous media approach while the droplets are modelled in a Lagrangian framework. Intense interactions are observed between the evaporating droplets and hot particles during contac...
This paper reports on the collision interaction between a confined liquid film (water) and an impacting hydrophilic glass particle of different diameters (1.1-2mm) and impact velocities (0.2-1 m/s). Depending on the impact Weber number... more
This paper reports on the collision interaction between a confined liquid film (water) and an impacting hydrophilic glass particle of different diameters (1.1-2mm) and impact velocities (0.2-1 m/s). Depending on the impact Weber number (1.4-23.9) of the particles either complete capture of the particle inside the film or complete penetration through the film were observed. In the latter case a certain amount of liquid mass was found to adhere to the particle surface which again depended on the impact Weber number. A criterion was developed based on the energy balance approach to demarcate between these two regimes. Also, an analytical model was proposed to approximately determine the liquid mass attached to the particle. Computationally, a three dimensional CFD model was developed using the VOF approach and dynamic meshing technique which was found to be in good agreement with the experimentally observed dynamics in these two regimes.
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Numerous works have been reported on the evaporation of a sessile liquid marble, a liquid droplet coated with particles, through geometric measurements. The lack of gravimetric measurement limits further understanding on the physical... more
Numerous works have been reported on the evaporation of a sessile liquid marble, a liquid droplet coated with particles, through geometric measurements. The lack of gravimetric measurement limits further understanding on the physical changes of a liquid marble during the evaporation process. Furthermore, the evaporation process of a marble containing a liquid binary mixture has not been reported. This paper studies the effective density and effective surface tension of an evaporating liquid marble which contains aqueous ethanol at relatively low concentrations. The effective density of an evaporating liquid marble is determined from the instantaneous mass and volume measurements. Subsequently, density measurements combined with surface profile fitting provides the instantaneous effective surface tension of the marble. We found that the density and surface tension of the evaporating marble is greatly affected by the particle coating.
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Research Interests: Mechanical Engineering, Chemical Engineering, Chemistry, Modeling, Nanoparticle, and 15 moreDensity, Dielectrophoresis, Diffusion, Ph, Aggregate, Difusion, Dep, Coordination number, Fractal Dimension, Experimental Data, Electric Field, Particle Number, Colloidal Suspension, Nova, and Isoelectric point
Multiphase systems are ubiquitous in industrial applications aimed at the generation of products either by chemical/biological reaction or physical separation based on density, electrical charge or surface properties such as... more
Multiphase systems are ubiquitous in industrial applications aimed at the generation of products either by chemical/biological reaction or physical separation based on density, electrical charge or surface properties such as hydrophobicity. The physical processing of these multiphase systems is carried out at all scales of operation and within an endless variety of vessel shapes and ancillary devices. Underpinning each process is a complex interaction between phases involving hydrodynamic, heat and mass transport. These phenomena are in turn governed largely by the nature of the flow, and in particular whether laminar or turbulent conditions prevail. In large-scale industrial processes the flows are almost always turbulent, whilst for microscale operations the flow will be laminar. Each condition provides its own challenge in being able to predict (and optimise) performance in terms of operational stability and efficiency of energy utilisation. Turbulent systems are particularly dif...
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ABSTRACT In this study the transition from homogeneous to heterogeneous flow in a solid–liquid fluidized bed (SLFB) is examined both experimentally and numerically. The experimental apparatus comprised a refractive index-matched SLFB,... more
ABSTRACT In this study the transition from homogeneous to heterogeneous flow in a solid–liquid fluidized bed (SLFB) is examined both experimentally and numerically. The experimental apparatus comprised a refractive index-matched SLFB, comprising 5 mm diameter borosilicate glass and sodium iodine solution, which allowed for both instantaneous particle image velocimetry of the liquid flow field and solids hold-up measurements to be undertaken for superficial liquid velocities in the range of 0.06–0.22 m/s. The motion of individual, spherical steel balls (with diameters 6, 7, 8, 9 mm) was then tracked as it settled through the fluidized bed for differing superficial liquid velocities. It was observed that, for all the steel balls covered in this work, there was a change in slope in their respective classification velocity curves at a superficial liquid velocity of 0.08 m/s. This value was very close to the critical velocity of 0.085 m/s predicted from 1-D linear stability analysis; and therefore deemed to be the critical condition that marked the transition from homogeneous to non-homogenous flow. It is proposed that the change in slope of the classification velocity curve is due to the encounter of the settling foreign particles with liquid bubbles whose presence marks the onset of heterogeneous flow. Additional computational analysis, involving both Eulerian–Eulerian (E–E) and Eulerian–Lagrangian (E–L) approaches, is used to confirm the presence of liquid bubbles at a critical liquid hold-up of 0.54, which corresponds to that predicted from 1-D linear stability analysis. In summary, the study has highlighted that experimentally the transition condition for a SLFB can be obtained simply by observing the behavior of the classification velocity of a single foreign particle at different superficial liquid velocities. This transition condition was found to agree with the 1D linear stability criterion, Eulerian–Eulerian CFD (3D) and Eulerian–Lagrangian DEM (3D) approaches.
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ABSTRACT Packed and fluidised beds in microfluidic devices offer the potential of enhanced heat and mass transfer capability at a scale where the process can be closely controlled. The knowledge of hydrodynamics of packed and fluidised... more
ABSTRACT Packed and fluidised beds in microfluidic devices offer the potential of enhanced heat and mass transfer capability at a scale where the process can be closely controlled. The knowledge of hydrodynamics of packed and fluidised beds in capillary tubes is essential for the design and optimization of such devices. This study experimentally examines the hydrodynamics of packed and fluidised beds in terms of pressure drop, bed expansion and minimum fluidisation velocity in tube sizes with inner diameters of 0.8, 1.2 and 17.1mm. Specifically the influence of the wall on the hydrodynamic characteristics of the beds was examined by changing the tube-to-particle diameter ratio.It was found that as the tube diameter reduces the bed voidage sharply increases leading to a reduction in the pressure drop across the bed. Also a pressure drop overshoot was observed at lower tube-to-particle diameter ratios which found to be associated with contact stresses due to wall friction.
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Research Interests: Engineering and COLLISION
Droplet evaporation in fluidized beds is of great interest in applications like fluidized catalytic cracking units. Although a significant number of analyses are available for modelling of droplet vaporization in a fluidized bed, very... more
Droplet evaporation in fluidized beds is of great interest in applications like fluidized catalytic cracking units. Although a significant number of analyses are available for modelling of droplet vaporization in a fluidized bed, very little work has been performed experimentally to measure the vapour concentration followed by numerical validation. In the present work, acetone droplet evaporation in a bubbling fluidized bed is studied experimentally as well as numerically. A liquid jet of acetone is injected into a hot bubbling fluidized bed kept well above saturation temperature of acetone. Nonintrusive Schlieren imaging, based on the difference in refractive index, is used to trace the acetone vapour concentration profile. The bubbling fluidized bed is modelled in an Eulerian framework using a simplistic porous media approach while the droplets are modelled in a Lagrangian framework. Intense interactions are observed between the evaporating droplets and hot particles during contac...
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Dynamic surface wetting of particles in contact with droplet is a complex phenomenon ubiquitously encountered in many multiphase systems of industrial importance. In this study, we address this aspect by investigating impact behavior of a... more
Dynamic surface wetting of particles in contact with droplet is a complex phenomenon ubiquitously encountered in many multiphase systems of industrial importance. In this study, we address this aspect by investigating impact behavior of a water droplet (diameter = 2.9 ± 0.1 mm) in the Weber number () range from ~4 to 104 on a stationary spherical brass particle (diameter = 10 mm) with and without heat transfer using a combination of high speed imaging and computational fluid dynamics (CFD) modeling approach. In cold state interactions (20°C), droplet exhibited oscillatory interfacial motion comprising periodic spreading and recoiling motion. Interactions involving heat transfer were studied in film boiling regime (350°C) and two outcomes were noted-droplet rebound and disintegration. A coupled Level Set and Volume of Fluid (VOF) approach based multiphase CFD model was utilized to predict the dynamic spread ratio and transient evolution of droplet shape during the interaction. To cap...
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ABSTRACT In almost all mineral flotation systems the particles and bubbles are brought into contact with each other under turbulent flow conditions which although beneficial in promoting particle-bubble collisions, at the same time... more
ABSTRACT In almost all mineral flotation systems the particles and bubbles are brought into contact with each other under turbulent flow conditions which although beneficial in promoting particle-bubble collisions, at the same time increases probability of particle detachment. Often the detachment of particle is described in terms of modified Bond number (expressed as ratio of attachment force to detachment force) greater than 1.0 however very few studies include attachment force in the numerical modelling. Acknowledging the dynamic interaction of bubble-particle aggregate in actual floatation system, in this work, a dynamic model of the particle motion on the bubble interface was developed based on Schulze’s theory considering contributions from gravity, buoyancy, pressure force, capillary force and the fluid drag. The purpose of this modelling was to check the consistency of the particle detachment criterion at Bond number greater than 1.0. Transient magnitudes of the both attaching and detaching forces were presented and the resulting temporal variation of the Bond number was reported. It was found that during the process of particle motion, although Bond number exceeded the limiting value of 1.0, particle still remained attached to the bubble interface. It appears that the criterion holds good only for steady state case when Bond number remains less than 1.0 and not for dynamic case where Bond number may exceed 1.0.
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In this study, microwave irradiation was applied to hanging droplets of both water and ethylene glycol. Once the irradiation had ceased and the droplet was allowed to return to its original temperature, it was found that the surface... more
In this study, microwave irradiation was applied to hanging droplets of both water and ethylene glycol. Once the irradiation had ceased and the droplet was allowed to return to its original temperature, it was found that the surface tension of ethylene glycol returned to its original value. In contrast, the water surface tension remained well below its original value for an extended period of time. Similar observations have been reported for magnetically treated water, but this is the first time that such a lasting effect has been reported for microwave irradiation. The effect can be attributed to the unique hydrogen bonds of interfacial water molecules. While the irradiation intensities used in this study are well above those in household devices, there is certainly the potential to apply the methodology to industrial applications where the manipulation of surface tension is required without the use of chemical addition.
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The Jones-Ray effect is shown to be governed by a different mechanism to enhanced anion adsorption. Halide ions at sub-molar concentrations are not exposed to the vapour phase; instead their first-solvating shell intimately interacts with... more
The Jones-Ray effect is shown to be governed by a different mechanism to enhanced anion adsorption. Halide ions at sub-molar concentrations are not exposed to the vapour phase; instead their first-solvating shell intimately interacts with the outmost water layer. Our novel proposal opens challenges for predicting related interfacial phenomena consistently.
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the hydrodynamics and recirculating flow characteristics of a reactor geometry consisting of a sudden expansion followed by a tapered contraction have been studied using the computational fluid dynamics package CFX-F3D. The results... more
the hydrodynamics and recirculating flow characteristics of a reactor geometry consisting of a sudden expansion followed by a tapered contraction have been studied using the computational fluid dynamics package CFX-F3D. The results provide important information for the design and optimization of such reactor configurations. The pressure difference across the reactor can be well predicted based on a simple theory derived from first principles. The value of ΔPR is strongly dependent on both the Reynolds number and inlet ...
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The effect of using small-scale, high surface area, nanoparticles to supplement polymer-conditioned wastewater sludge dewatering was investigated. Aerobically digested sludge and waste activated sludge sourced from the Hunter Valley, NSW,... more
The effect of using small-scale, high surface area, nanoparticles to supplement polymer-conditioned wastewater sludge dewatering was investigated. Aerobically digested sludge and waste activated sludge sourced from the Hunter Valley, NSW, Australia, were tested with titanium dioxide nanoparticles. The sludge samples were dosed with the nanoparticles in an attempt to adsorb a component of the charged biopolymer surfactants present naturally in sludge. The sludge was conditioned with a cationic polymer. The dewatering characteristics were assessed by measuring the specific resistance to filtration through a modified time-to-filter testing apparatus. The solids content of the dosed samples was determined by a mass balance and compared to the original solids content in the activated sludge. Test results indicated that nanoparticle addition modified the structure of the sludge and provided benefits in terms of the dewatering rate. The samples dosed with nanoparticles exhibited faster water removal, indicating a more permeable filter cake and hence more permeable sludge. A concentration of 2-4% nanoparticles was required to achieve a noticeable benefit. As a comparison, the sludge samples were also tested with a larger particle size, powdered activated carbon (PAC). It was found that the PAC did provide some minor benefits to sludge dewatering but was outperformed by the nanoparticles. The solids content of the final sludge was increased by a maximum of up to 0.6%. The impact of the order sequence of particles and polymer was also investigated. It was found that nanoparticles added before polymer addition provided the best dewatering performance. This outcome was consistent with current theories and previous research through the literature. An economic analysis was undertaken to confirm the viability of the technology for implementation at a full-scale plant. It was found that, currently, this technology is unlikely to be favourable unless the nanoparticles can be sourced for a low cost.
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The aim of this study was to better understand flow characteristics in the taphole stream impingement region of a blast furnace trough, and its effect on localized trough refractory wear. A 1/5th scale perspex model was used, and oil and... more
The aim of this study was to better understand flow characteristics in the taphole stream impingement region of a blast furnace trough, and its effect on localized trough refractory wear. A 1/5th scale perspex model was used, and oil and water were adopted to simulate the molten iron and ...